1. Field of the Invention
The present invention relates to a dental articulator used in preparing a new denture from an existing denture. More particularly, the present invention relates to the structure of a dental articulator capable of preparing the new denture from the existing denture on the basis of features of a patient's jaw joint which is wide in allowance in relative movement between a lower jaw and an upper jaw of the patient, wherein the new denture is free from any feeling of physical disorder even when it is new for the patient, wherein the dental articulator may reproduce the patient's dental arches in the patient's oral cavity, wherein the dental arches are precise in occlusion height in the oral cavity defined between the lower and the upper jaw and heretofore neatly fit to the patient in use. Further, the present invention relates to both a method for producing a new denture and a method for adjusting the occlusion height of the dental articulator in preparing the new denture from the existing denture.
2. Description of the Related Art
As shown in FIG. 16, a conventional dental articulator 1 (for example, such as one disclosed in Japanese Patent application Laid-Open No. Hei 9-206315) comprises: an upper frame 13 provided with an upper jaw model supporting portion 11 which is formed in a so-called “Frankfort plane”, mounted on which supporting portion 11 is an upper jaw model 10; a lower frame 23 provided with both a lower jaw model supporting portion 21 and a front end portion on which an incisal table 22 is mounted, mounted on which supporting portion 21 is a lower jaw model 20; a stand portion 30 for supporting both the upper frame 13 and the lower frame 23 in a manner such that a distance between the upper frame 13 and the lower frame 23 is adjustable by adjusting these frames 13, 23 independently of one other in position, which distance is hereinafter referred to as “occlusion height”; and, an incisal pin 14 which is mounted on the upper frame 13 so as to have its lower end portion disposed adjacent to an upper surface of the incisal table 22.
In the conventional dental articulator 1 having the above construction, the upper jaw model supporting portion 11 and the lower jaw model supporting portion 21 are detachably mounted on the upper frame 13 and the lower frame 23, respectively.
On the other hand, the dentures thus prepared become worn during daily mastication of meals. Consequently, it is necessary for the patient to replace the thus worn dentures with new ones every few years.
In preparing a new denture based on the patient's existing (i.e., old or worn) denture 50 by using the dental articulator 1, an old upper denture 51 has its border (i.e., peripheral portion) extended upward (as viewed in FIG. 1) to form a dam by the addition of is compound material. Then, the old upper denture 51 provided with the dam in its border is returned to the patient oral cavity, so that the dam of the old upper denture 51 is brought into contact with the mucous membrane of the patient's oral cavity and deformed by the pressure of the membrane to become neatly fit to the patient's oral cavity. Hereinafter, a process step for forming and modifying in shape the dam of the modified old denture is referred to as a “dam formation” step. The old upper denture 51 having been subjected to the “dam formation” step is then used as an upper dental tray 51. In use, the upper dental tray 51 thus prepared has its entire tissue side loaded with an impression material in order to obtain the impression of a mucous membrane of the patient's oral cavity when returned into the patient mouth. Likewise, an old lower denture 52 is modified in shape in a manner similar to the modification of the old upper denture 51 to become a modified old lower denture 52 capable of serving as a lower dental tray 52, as viewed in FIG. 1.
After the impression material loaded on the tissue side of the modified old upper denture 51 (which serves as the upper dental tray) has set or hardened, gypsum is poured in an oral cavity side of the modified old upper denture 51 to take the impression of the teeth and gum of the old upper denture 51. After the gypsum has set or hardened, the hardened gypsum is taken out of the old upper denture 51 to become an upper negative gypsum model of the teeth and gum of the modified old upper denture 51. Likewise, a lower negative gypsum model of the teeth and gum of the modified old lower denture 52 is made in a manner similar to the making of the upper negative gypsum model.
After that, a paraffin wax is poured into the upper and the lower negative gypsum model to produce an upper and a lower wax positive model, respectively.
The wax positive models having been softened by heating are then inserted into the patient's oral cavity and subjected to a so-called “occlusion confirmation” process in which the wax positive models are corrected in shape in occlusion action. In the thus corrected wax positives, now, their wax teeth are replaced with pre-cast more rigid prosthetic teeth having been selected by the patient in type, size and shade, so that a so-called “occlusion bite pieces” are prepared. The occlusion bite pieces form pre-forms of the new dentures.
Added to the thus prepared pre-forms of the new dentures are gum portions to complete the pre-forms.
By using the thus completed pre-forms in a so-called “immersion process”, negative molds of the new dentures are prepared. More specifically, the substitution of a suitable resin material for the wax gum portion of each of the completed pre-forms is carried out by a conventional lost wax process known in the art (see, Jun Nishiura, “dental technique for a denture with a base, general denture version”, I-Shi-Yaku Shutzpan Kabushiki Kaisha, May 20, 1976, pp. 33–112).
Problems to be solved by the present invention will be now described.
In the conventional method for producing the new denture, however, there is no standard in occlusion height (i.e., precise height in occlusion) in the oral cavity in conducting the so-called “occlusion confirmation” process in which the wax positive models are corrected in shape during the occlusion action. Heretofore, the occlusion height is determined by individual dentist's experience. This leads to frequent modifications of the new dentures in shape after delivered to the patients.
In other words, in the oral cavity side of the new denture, it is possible to utilize the information obtained from the old denture as to a dam formed in a border portion of the new denture. In contrast with this, in the tissue side of the new denture, it is not possible to utilize any information obtained from the old denture as to the occlusion height in the patient's oral cavity. Further, since a new set of artificial teeth are embedded in the dental arch of the new denture, it is necessary for the patient to return many times for follow-up appointments in order to have the dentist reshape and reconfigure the new denture so that it seats properly in the patient's mouth and feels correct to the patient. Such multiple return visits to the dentist office are not only annoying to the paying customer (i.e., patient), but also cost the dentist time and money, reduce patient confidence in the dentist, and, occasionally, one losses the patient's patronage.
The old dentures are useful in preparing the new dentures since the old dentures have been used actually for a long period of time by the patient, and therefore have a plenty of helpful information as to the new dentures. Therefore, it is very important to utilize the information obtained from the old dentures in preparing the new ones.
As for the conventional dental articulator having the above construction, it is not possible for the conventional dental articulator to compensate for the amount of wear in the teeth portion of the old denture in setting the occlusion height in the patient's oral cavity between the upper jaw model and the lower jaw model. This makes it impossible to prepare the new dentures on the basis of the old dentures, particularly, their occlusion conditions. More particularly, in the conventional dental articulator, it is not possible to move the upper and the lower jaw model in parallel with each other when the incisal pin 14 is adjusted to compensate for the amount of wear of the old dentures. Further, the incisal pin 14 may adjust a distance between the upper and the lower jaw model in their front end portions only. Due to these facts, an occlusion height (i.e., distance between the front end portions of the jaw models) is different from another occlusion height (i.e., distance between the rear end portions of the same jaw models) in the same patient mouth. This leads to improper occlusion state in the patient's oral cavity.
Further, in the conventional dental articulator, by adjusting its stand portion 30 in length, it is possible to adjust in distance between the upper frame 13 and the lower frame 23. However, since the amount of wear of the upper jaw model 10 is often different from that of the lower jaw model 20, it is not possible to set a proper occlusion height even when the stand portion 30 is adjusted in length. Due to this, it is not possible for the conventional dental articulator to properly set each of the upper jaw model 10 and the lower jaw model 20, i.e., not possible to reproduce the actual occlusion conditions of the upper jaw model 10 and the lower jaw model in the patient's mouth.
In other word, in the conventional dental articulator, the jaw joint is realized in motion only by means of the incisal pin 14 as to the occlusion height in the patient's oral cavity. However, the jaw joint is different from any other joints since the jaw joint permits both the upper jaw and the lower jaw to move independently of one other in every direction by approximately 4 mm at maximum. Consequently, the teeth of the dentures are worm in mastication of everyday meals and therefore reduce in height. Due to this, the jaw joint loses its tightness. The inventor of the present invention has found the fact that the teeth of the dentures are substantially evenly worn in the same horizontal plate. This finding leads to the conclusion that: in preparing a new denture from an existing or old denture, since the conventional dental articulator can't conduct any balanced adjustment in occlusion height due to its utter lack of consideration regarding the jaw joint's freedom in motion, it is not possible to prepare any new denture excellent in occlusion state.